It's possible the murderer represents a part of yourself who feels threatening. It may also be that you fear death -- dreams are good at finding images that have multiple meanings. Although it seems scary to contemplate that your psyche has a "murderer" in it, it's actually a common thing that a lot of people have... it can develop as a defense mechanism against feelings that are threatening.

Whatever this murderer symbolizes, your dream self is showing it to you because it feels you are ready to see this image. Take courage.